When processing materials in particular in metal cutting machining, high demands are made on the corresponding tools. These include wear resistance and depending on the respective purpose of use corresponding hardness, toughness and temperature resistance. To provide those properties tools are generally made from a main body (substrate) of hard metal, cement, steel or hard speed steel with a coating of metallic hard substances, oxide layers or the like with high wear resistance and suitable adhesive and cutting properties. Those coatings be applied using a CVD process (chemical gaseous phase deposition) or a PVD process (physical gaseous phase deposition). In regard to the PVD processes different variants are used for vapor deposition of the material to be deposited. PVD processes with cathode sputtering (sputter deposition), arc vapor deposition (arc PVD), magnetron sputtering, reactive magnetron sputtering and high power impulse magnetron sputtering (HPIMS) are frequently used for coating tools.
An advantage of magnetron sputtering is that vaporisation or sublimation of the target involves fine detachment of particles and that produces a fine coating. A disadvantage of that process however is that the necessary process gas flow is difficult to regulate. In addition in the deposition of aluminum oxide layers in the magnetron sputtering process there is the disadvantage that only relatively small amounts of the particularly preferred wear-resistant alpha phase are deposited.
In contrast thereto in the PVD coating procedure using the arc vapor deposition process (arc PVD) by virtue of high ion energy levels in the deposition of aluminum oxide layers it is possible to achieve a high proportion of the alpha phase in the coating. In that process the arc generates on the target very high temperatures of the order of magnitude of several thousand degrees Celsius which lead to the desired vaporisation or sublimation of the target material for deposition on the substrate. Around the point of impingement of the arc however there are zones of lower temperature for example in the region of 500 to 1000 C in which in the case of some target metals detachment of macroparticles occurs, so-called droplets, which are also deposited on the substrate. Such droplets are responsible for an unwanted roughness of the deposited layer in comparison with layers produced by magnetron sputtering. In addition the droplets cause weakening of the coating as they are generally predominately purely metallic and thus present a low level of hardness and tendency to oxidation.